1. Field of the Invention
This invention relates to an apparatus and method for thermally controlling deposition in Dip-Pen Nanolithography, or DPN (Dip-Pen Nanolithography, and DPN are registered trademarks of Nanoink).
2. Description of the Prior Art
The ability to create ever smaller structures and patterns is the key to producing smaller and faster electronics. Some of the newest technologies allow the creation of structures on the nanometer, or 10−9 meter, scale. One of these technologies is DPN, which is described in U.S. Pat. No. 6,635,311 and is incorporated herein by reference (all patent and publication references included in this specification hereinafter are also incorporated by reference). DPN is a method for depositing molecules onto a surface with the tip of an atomic force microscope (AFM). The method is very much like dipping a pen into an inkwell and then using it to write except DPN is on a much smaller scale. In DPN, the AFM tip, or “pen,” is dipped or coated with the desired molecule or “ink” and then brought into contact with the surface, onto which the molecules diffuse. Lines or patterns can be created by moving the tip over the surface in much the same way one would move a pen over paper.
With this technology, however come some limitations. When writing with a pen on paper one must lift the pen to stop writing. The same is true for DPN; to stop deposition the AFM tip must break contact with the surface. Unfortunately, this can often lead to a loss of registry between the tip and the surface. Another drawback to DPN is that a coated tip cannot be used for imaging purposes while in contact mode without causing contamination—deposition of unwanted ink. Therefore, a need exists for a device that can turn deposition on or off while the tip maintains contact with the surface.
DPN is further limited in that besides changing the ink, the tip, or the tip's speed, there is little control over the deposition rate once a molecule has been coated onto the tip. The typical ink molecules utilized in DPN have to be sufficiently mobile to transfer from the AFM tip to the surface under ambient conditions. This ambient temperature mobility requirement limits the types of inks that may be used in DPN and results in “bleeding” or spreading out of the ink once it is deposited onto a surface, which in turn limits the precision of structures that can be created with DPN. Because of this necessary volatility of the inks used in DPN, the process cannot be performed in a vacuum; the ink would evaporate too quickly and contaminate the system. The need exists for a better method that may be performed in a vacuum and that allows for the use of a greater variety of inks. A better method is also needed to control the rate of deposition and to limit the excess diffusion of molecules over the surface after deposition.
Information relevant to attempts to address these problems can be found in U.S. Pat. Nos. 6,737,646 and 6,642,129. However, each one of these references suffers from one or more of the following disadvantages: inability to image in contact mode without contaminating, inability to turn deposition on or off, and inability to control excess diffusion of ink once deposited. For the foregoing reasons, there is a need for a process of turning ink deposition on and off in DPN without breaking contact between the tip and the surface. Likewise, there is a need for an apparatus that can control the ink deposition rate and limit the amount of excess ink diffusion or contamination over the surface.